This study proposes to investigate the initial immune response at the primary site of influenza virus infection, and how the cytokine response by these cells may alter the role of peripheral leukocytes that are initially isolated from the virus. We first propose an in depth characterization of the reponsive lung population through careful dissection of individual cell populations in the lung via flow cytometric sorting. These populations will then be individually analyzed by quantitative PCR along early infection time points, but also in their full tissue context by fluorescent microscopy. We also hypothesize that the lung-derived cytokines that characterize the early immune response serve not only in chemotaxis of blood leukocytes, but also to prime these cells for antiviral immunity. Of particular interest is the monocyte, which is able to serve as a precursor to both dendritic cells and alveolar macrophages, two cells that are important for viral immunity. Through a battery of functional and analytical tests, we propose to characterize this priming state in monocytes and how it may improve the immune response to the influenza virus. Lastly, we will analyze the role of primed monocytes as they infiltrate the lung, and track their fate in the context of an influenza infection. We hypothesize that peripheral leukocytes in general, and monocytes in particular, are significant effector cells distinct from resident lung leukocytes due to their isolation from primary infection, and exposure to antiviral priming cytokines. Ultimately, the goal of this research is to provide a better understanding of immunity to respiratory viral infection. In this proposal, we hypothesize the existance of a novel mechanism by which the immune system is able to circumvent viral defenses. This work will further our understanding of the pathology of influenza infection as well provide insights into novel therapeutic interventions, and potential novel vaccine strategies.